The present invention relates to a storage system.
One known prior art technique (hereinafter referred to as prior art technique 1) described in Japanese Patent Laid-Open No. 11-167521 (1999) employs a common bus system so that logical modules, such as host adapters and storage adapters, as well as cache memories and disk devices can be added to the system according to the system configuration (scale), creating a scalable storage system. In this storage system, each logical module, disk device, and common bus are multiplexed, enabling an operation in a degraded mode, “hot-plugging” of the logical modules and storage media, and hence maintenance of the system without a system shutdown.
Many of the disk control devices disposed between hosts and disk devices for controlling data transfer therebetween, such as those employed by the above prior art technique 1, each include a cache memory for temporarily storing data to be transferred. However, since this cache memory is a volatile memory, the data in it disappears when the power supply is stopped. Furthermore, the data may be lost due to a failure in the cache memory hardware in the disk control device. To prevent such data loss, a known disk control device includes duplexed cache memories and stores write data in them. Even with such a configuration, however, data will be lost in the event of a double cache failure.
The above prior art technique 1 also employs a redundant power supply in addition to a primary power supply, and thereby the system can continue to operate even when one of them has failed. Furthermore, the standby power supply provided for the disk control devices allows prevention of data loss in the cache memories and the shared memories in the event of a power failure. Specifically, when a failure has occurred in the power supply, the dirty data in the cache memories is saved to the disk devices so that data in the cache memories is reflected in them.
If a write request is issued from a host after such a failure handling operation, a synchronous write operation is carried out in which a write completion notification is sent to the host after the write data has been written to a disk device, in order to ensure data integrity. The synchronous write operation, however, has the problem of exhibiting reduced response to the host, as compared with the “write-back” method.
Another known prior art technique (hereinafter referred to as prior art technique 2) is disclosed in Japanese Patent Laid-Open No. 2002-334049. Prior art technique 2 limits the quantity of side files input to the storage subsystem subordinate to a plurality of hosts which performs asynchronous remote copy operations. This limit operation is achieved by setting a priority for each host and thereby preventing data with a low importance level from occupying the greater part of the cache memories.
Still another known prior art technique (hereinafter referred to as prior art technique 3) is disclosed in Japanese Patent Laid-Open No. 2003-6016. In asynchronous remote copy operation, prior art technique 3 sets a copy priority for each logical volume group and performs copy operation on these logical volume groups in order of priority.